What is Long QT Syndrome?

Long QT syndrome (LQTS) is a medical condition caused by a problem in the electrical system of the heart. 

The "QT" interval is a measurement on an electrocardiogram (ECG), which shows the heart's electrical activity. It measures the time it takes for the heart to start a beat and then get ready for the next one. The QT interval is measured in seconds or milliseconds. 

A "long QT" means the interval is longer than usual. This happens when the heart's lower chambers (ventricles) take longer to recharge. It can cause an abnormal heart rhythm (arrhythmia), which can be dangerous. Some QT intervals are borderline and still normal. Long QT syndrome (LQTS) happens when the QT interval is unusually long and can lead to symptoms like fainting or sudden cardiac arrest.

In most cases, LQTS is caused by a genetic mutation that is passed down through a family. It can also be caused by certain medications. LQTS can show up in different forms and can be hard to diagnose. 

Signs and symptoms of Long QT Syndrome

LQTS can cause: 

• Fainting, especially with strong emotions (like anger or surprise), exercise, menstruation or swimming
• Seizures (not caused by epilepsy)
• Abnormal heart rhythms in the lower chambers of the heart (called ventricular arrhythmias)
• Sudden cardiac arrest

Sometimes children or adults have no symptoms until they experience sudden cardiac arrest.

Testing and diagnosis of LQTS

If a child has repeated fainting episodes or other symptoms, a pediatrician may refer them to a pediatric cardiologist. Many children with LQTS don’t have symptoms until their teenage or young adult years. To determine if your child has LQTS, your doctor may use a Holter monitor which is a wearable device that records the heart’s electrical activity, and an exercise stress test. Because LQTS is usually inherited, your cardiologist may consider genetic testing and counseling. Genetic testing may help confirm the diagnosis, but not all genes can be found yet, so the test could come back negative even if your child has LQTS. 

If your child is diagnosed with LQTS, siblings, parents, and other family members may also have it. At Children’s Hospital of Philadelphia (CHOP), your child’s cardiologist will talk to you about these risks and discuss steps to address them, including testing the entire family for LQTS. 

Treatment for Long QT Syndrome

Treatment for LQTS depends on which type of the condition your child has. 

Children with LQT1 are more likely to have symptoms with exercise but can sometimes have symptoms with strong emotions or even while resting. LQT1 can usually be treated effectively with medications called beta blockers, which help lower the chances of heart problems like arrhythmias and sudden cardiac arrest. Keeping normal potassium levels and following any lifestyle modifications your cardiologist recommends are also very important. 

Children with LQT2 are more likely to have symptoms with strong emotions but can also have symptoms during exercise and when resting. LQT2 can often be treated well with beta blocker medication, but keeping potassium levels normal can also help. Children with LQT2 are the group most affected by medications that can make the QT interval longer. Check this site for what medications to avoid. Loud sounds like doorbells and alarms can also trigger symptoms and should be avoided as much as possible. 

Children with LQT3 are more likely to have symptoms during rest. Beta blocker medications are less effective in some children with this type of LQTS, and some may need to take additional medication. Some children with LQT3 may need an implantable cardioverter-defibrillator (ICD). This device works like a pacemaker and can stop arrhythmias and reset the heartbeat. Getting this device requires surgery.

It’s important that all children with LQTS have access to an AED (automated external defibrillator) at home, school and on the playing field. Family members, teachers and coaches should know how to use the AED and how to perform CPR (cardiopulmonary resuscitation).

It is particularly dangerous for a child with LQTS to have low levels of electrolytes (such as sodium and potassium). Staying hydrated with water and sports drinks containing electrolytes is very important before, during and after exercise. 

Youth Heart Watch at CHOP works toward ending sudden cardiac death through research, education, prevention and advocacy. The program’s goal is to have a life-saving AED in every school in Pennsylvania, New Jersey and Delaware, with access to every child’s playing field or sports event.

Outlook for LQTS

If your child has LQTS and isn't treated, the risk of sudden death is high. However, most people with LQTS live normal, healthy lives. It's important for families to recognize the signs of sudden cardiac arrest and know how to use an AED and perform CPR to get help right away.

Follow-up care for LQTS

Children with LQTS will need to continue their medication and other treatment for the rest of their lives. They will also require lifelong care by a cardiologist. In most cases, one or two checkups each year is enough.

Our pediatric cardiologists follow patients until they are young adults. The Philadelphia Adult Congenital Heart Center, a joint program of CHOP and Penn Medicine, meets the unique needs of adults who were born with heart defects. 

At CHOP’s Cardiac Center, we support our adolescent and young adult patients through a smooth and seamless transition to adult cardiology care at the Philadelphia Adult Congenital Heart Center or, if desired, to a cardiologist with congenital heart disease expertise in another location.